Sciencemadness Discussion Board - Homemade diaphragms for electrolysis. New developments

Homemade diaphragms for electrolysis. New developments

Hexabromobenzene - 13-9-2024 at 12:16

Many electrochemical syntheses require a diaphragm. However, there is very little information on amateur simple, cheap and reliable diaphragms on the Internet. I decided to fix this. Amateurs use clay pots as a diaphragm, but they are expensive, heavy and conduct electricity poorly

I read the instructions mysteriusbhoice and decided to develop my own diaphragms. The basic material for them is meltblown polypropylene fabric as well as any CYLINDRICAL container made of polyethylene or polypropylene (bottles, glasses, cans, etc.) on which you will wind this fabric.

The basic manufacturing technique is as follows: Using an electric soldering iron, many holes are made in a circle in a plastic container, then the container is sanded with sandpaper to remove irregularities. Next, you wind the polypropylene fabric in several layers. After that, you make ropes from the same fabric and wrap this fabric on top with considerable force and fix it with a knot. This is very important. Without a strong fit, your diaphragm will leak.
And so you got a raw diaphragm. In this state, it is not a diaphragm but rather a filter. There are several ways to make this a diaphragm.

The most universal way is to wrap with a separator from of lithium-ion batteries the container BEFORE wrapping with polypropylene fabric. I do not recommend separators from automotive lead batteries. These separators have poor geometry and are difficult to seal hermetically.

You can use such a diaphragm for organic and inorganic electrosynthesis. Polypropylene is resistant to acids, alkalis and organic solvents.

The second way is to soak the polypropylene fabric with a polymer solution and remove the solvent with water. This is what did mysteriusbhoice. The downside of this method is that even such a durable plastic as PVC can be destroyed by organic solvents. Other varnishes and polymers are much less durable. I did it this way: The workpiece for the diaphragm with polypropylene fabric was impregnated with varnish from old paint with settled filler. Afterwards, the workpiece was immersed in a bucket of warm water with washing powder while actively stirring. Then the wet workpiece was wrapped on top with new ropes made of polypropylene fabric and dried
With these actions, you reduce the porosity of the diaphragm, but the polymer filler usually has lower chemical resistance than polypropylene.

The last way is inorganic fillers. You can soak the workpiece with sodium silicate and add any acid. This way you will get a diaphragm for working with organic substances and an acidic medium. For an alkaline medium you can use sodium hydroxide with magnesium sulfate or calcium salts instead acid for silicate percipation.
Inorganic fillers are resistant to any organic solvents and can be used for organic electrosynthesis. But they are sensitive to the pH of the environment.

Diaphragm test. The diaphragm should conduct current in salt solutions and not leak. Pour water into the diaphragm and leave it for about 10 minutes. It should not leak a significant amount of water. A small amount of liquid is acceptable. If too much water leaks, add ropes for fixation or soak it with fillers again.

P.S. If you preparing sulfuric acid by electrolysis of gypsum, you can not modify the polypropylene fabric. The gypsum layer is a diaphragm in itself

[Edited on 13-9-2024 by Hexabromobenzene]

Hexabromobenzene - 13-9-2024 at 12:41

Ion exchange resins are not discussed in this article. I have not found a way to make them from readily available materials. Non-crosslinked resins will not be chemically stable and will not be suitable for organic solvents. Sulfonated polystyrene would work well in theory for inorganic syntheses such as chlor-alkali cells. The manufacturing process is the same as with polymer filler.

Sample of workpiece on pic

[Edited on 13-9-2024 by Hexabromobenzene]

Hexabromobenzene - 27-9-2024 at 15:06

A more improved method for making porous diaphragm.
You no longer need solvents or adhesives anymore. Everything is very simple and cheap
You only need a polypropylene container and a piece of fabric meltblown. You can also make a container from a polypropylene pipe from the sewer weldind bottom with an electric soldering iron

Polypropylene blank with holes is wrapped with a piece of polypropylene fabric. Thin iron sheet is wrapped on top. Blank with fabric is fixed with a metal wire and heats up in the oven at 170-180 degrees for several minutes

Due to the temperature and pressure of the iron sheet, the layer of polypropylene becomes much less porous and is more like ceramics as we need. Diaphragm is very light, chemically persistent and cheap

The porous layer of plastic gets wet, but the water does not leak significantly

[Edited on 28-9-2024 by Hexabromobenzene]

Pumukli - 27-9-2024 at 21:22

Looks promising. Hats off, Hexabromobenzene!

I like it when I see people use simple everyday things and assemble them a way no one tried before! This polypropylene wrap thingy looks exactly like that.

The heat-treatment is also an interesting approach. Simple, cheap and with the critical timing and temperature it might provide a useful "toy" for us hobbysts.

Now I would like to see the characterization attempts of this gadget!

E.g: fill the cell with a known concentration of acid then determine the acidity (leakage) in the outer container at 1 hour increments. Draw a graph leaked acid versus time.

Or give us a number: leaked acid in an hour (in millimol/hour)
Or fill the cells (both compartments) with a known (one molar maybe?) salt solution (NaCl) and measure the electric resistance of this assembly with a DVM. This ohmic resistance value would be an interesting clue regarding the possible performance of the cell.
Or use this cell in a practical electrosynthesis and show us what can be achieved with such a "toy"!

Hexabromobenzene - 28-9-2024 at 09:04

I made the second according to the same technology. The temperature was increased to 180 degrees

The leak of water through the new backed diaphragm was 1 ml in 10 minutes. First noticeably more. Probably due to incorrect compression of an iron sheet during baking.

For conducting an electrochemical test, stainless spoons were used as electrodes, a strong solution of sodium chloride and 2 batteries(3 volts) AA as a source of current. Without diaphragm, the current of 400 mA. With backed diaphragm number 2 current about 30 mA.

The current of the first diaphragm was 3 mA. Current of another diaphragm without baking, but with a separator from lithium batteries was 2 mA

The volume of the diaphragms is 90ml.

A diaphragm without baking and without a separator from a post http://www.sciencemadness.org/talk/viewthread.php?tid=160566... with a volume of 400 ml shows a current of 20 mA

Definitely a working method, but more experiments are required.
During baking, the fabric is welded to the polypropylene container and you no longer need to fix it

Polypropylene is a wonderful material. Having an electric soldering iron, oven and electric stove can be made of various reactors, rectification columns, distillators. Operating temperature of polypropylene up to 120 degrees

[Edited on 28-9-2024 by Hexabromobenzene]

BlueSwordM - 22-10-2024 at 09:52

If you're interested, I found a website blog discussing of many electrochemical subjects, but the most interesting part to me was related to cation exchange membranes:
https://chemisting.com/2022/11/27/a-diy-cation-exchange-memb...

There's a whole series on this subject.
I've managed to replicate the first membrane and it works decently.

I'm slowly moving up the chain to replicate this results, but they're very promising.

Hexabromobenzene - 27-10-2024 at 10:49

Yes, it is a PVA ion exchange membrane. It is not chemically stable
I was able to find some ion exchange resin for water purification in the form of small balls. I will bake layer it between polypropylene fabric. It will be an analogue of ionic cement cement from mysteriusbhoice.

This ion exchange resin is very stable. It does not dissolve in dichloromethane and DMSO is resistant to alkalis and acids

semiconductive - 27-10-2024 at 14:54

I'm curious; I found porous cups on ebay and bought one to try and fix a tin-plating problem. Background of issue, mentioned here:

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

How badly do membranes tend to clog in your experience?
This is the one I bought, for example:

Attachment: membrane.webp (13kB)
This file has been downloaded 52 times

It Sstarted out as white and had 2Amps of current flowing at 36Volts applied to the tin anode inside the cup with titanium dioxide, boric acid and water in the anode compartment; Citric acid, and a steel target to plate were outside the cup, making the cathode portion (the bucket).

This does work, quite well. I can electroplate copper coins with tin, and get a very shiny smooth coating that's practically a mirror.

But, over the last week of use the current carrying capacity has dropped from 2Amps down to a measly 150 milliamps.

Increasing the conductivity of the solution by adding acid has no effect.

At first there were large white blocks of ceramic visible with small grey/black lines on it; I tried grinding them off and thinning the ceramic cup wall thickness; but slowly the ceramic has turned to what's shown in the picture over a week.

I have been happy with the fact that the membrane does not leak water except very slowly. Maybe a teaspoon in a week's use. So there's no degradation of the citric acid by electrolysis. Basically, I can wipe of a sponge of it from the ceramic filter and it keeps right on plating -- organics stay OUTSIDE the cup, ions pass through the cup, and I can use high anode voltages to get ions into solution.

But, how common is it to loose 92% of your current flow in a situation like I'm describing?

Since you're experimenting:
I bought some fish-tank bio-ceramic filters that have much larger pores, and was considering dissolving a little bit of cellulose acetate paper that I got on ebay to turn them into a membrane so I could compare how they performed to my ceramic cup. Another thought that occurred to me was to dissolve a bit of clear silicone caulk in a large quantity of ethyl acetate, in order to increase the chemical resistance/life of the cellulose acetate.

The plastics you are using -- do they completely block organic molecules from passing through; or are you just trying to mostly contain chemicals in separate chambers with it?

Can the plastics you've experimented with be dissolved, or are the pores mechanical in nature and unable to be coated? I don't think it would be too hard to wrap a bio-filter in plastic and cook at 180 in an oven. But, I'm curious as to how stable you think your membrane would be during tin plating?

(I know very little chemistry. I'm a BSEE -- so this is all learn by bumps, crashes, and braile.

) But I enjoy experimenting.

BlueSwordM - 27-10-2024 at 19:39

Quote: Originally posted by Hexabromobenzene

Yes, it is a PVA ion exchange membrane. It is not chemically stable
I was able to find some ion exchange resin for water purification in the form of small balls. I will bake layer it between polypropylene fabric. It will be an analogue of ionic cement cement from mysteriusbhoice.

This ion exchange resin is very stable. It does not dissolve in dichloromethane and DMSO is resistant to alkalis and acids

That is somewhat true, but further protocols designed membranes that are much tougher, as it seems the main bottleneck is in membrane chemical resistance rather than PVA.

This doesn't fix the issue of low pH performance, so it limits PVA CEMs to mainly neutral/high pH environments.

Hexabromobenzene - 28-10-2024 at 04:19

Polypropylene is resistant to solvents and you can't dissolve it in anything. Ion exchange resin is also resistant to solvents, even such as dichloromethane, because it is a cross-linked polymer

Water flows through the diaphragm at a rate of 10-20 ml per hour. You can reduce this by simply adding another layer of polypropylene, but the resistance will increase. Adding ion exchange resin will probably reduce the porosity and reduce the resistance. I hope.

The task of the diaphragm is organic and inorganic electrosynthesis. In my case, I just need to limit diffusion as much as possible without significantly reducing the current. I do not like diaphragm electrolysis. It requires more voltage, but the process occurs with less current. But sometimes there is no other choice.

Hexabromobenzene - 19-11-2024 at 00:21

Diffusion test. A solution of melanoidin was poured into the container with the diaphragm. In the second container, pure water. In the photo, the result of diffusion after 14 hours as well as a solution after direct mixing of the contents of 2 containers
The fluid level in 1 and in the 2nd vessel was the same.
The diaphragm is made by baking method

Pumukli - 19-11-2024 at 08:31

Looks promising.
Now, that you probably have something that would worth playing with, do you plan to use this membrane-setup for some sort of electro-synthesis?

Hexabromobenzene - 27-11-2024 at 08:00

Preliminary test showed a current up to 0.7a with 12 volts in a solution of salt. Other diaphragms do not conduct electricity. Probably a plastic layer is too thick

Apparently, the diaphragm leaks at the place of contact of porous plastic with the workpiece.

The addition of ion exchange resin did not improve conductivity but increased leaks.

The size of the pores in the meltblown fabric several micrometers but probably was reduced significantly when the plastic is flattened during backing